Anode modulated tube



M 21, 1942. B, QUNA'R. 2,290,377

ANODE MODULATED' TUBE Filed April 1, 1940 INVENTOR Patented duty 21,1942 AN ODE MODULATED TUBE Bartholomew Molinari, San Francisco, Calih,assignor to Farnsworth Television and Radio Corporation, a corporationof Delaware Application April 1, 1940, Serial No. 327,180

2 Claims.

. My invention relates to oscillograph tubes, and more particularly tosuch a tube that is operated with anode modulation.

Among the objects of my invention are: To provide a cathode ray tube anda circuit therefor for anode modulation of the tube; to provide a meansand method of preventing signal impulses from affecting beam focus; toprovide a means and method of maintaining scanning lines constant inwidth across light-dark boundaries of an image reproduced by scansion ina cathode ray tube; to prevent tailing out of scanning lines in acathode ray tube; and to provide a television receiving tube and circuittherefor, with means for reducing the effect of signal on beam focus.

My invention possesses numerous other objects and features of advantage,some of which, together with the foregoing, will be set forth in thefollowing description of specific apparatus embodying and utilizing mynovel method. It is therefore to be understood that my method isapplicable to other apparatus, and that I do not limit myself in any wayto the apparatus of the present application, as various other apparatusembodiments may be adopted utilizing the method, within the scope of theappended claims.

Referring to the drawing:

Fig. 1 is a simplified diagram of a circuit used in conjunction with thecathode ray tube of my invention, the tube being shown in section.

Fig. 2 is an enlarged view of the electron gun system utilized in myinvention My invention maybe more fully understood by direct referenceto the drawing, wherein a cathode ray tube having an envelope I isprovided at the large end thereof with the customary fluorescent screen2. At the other end of the envelope,'in a smaller cylindrical portion 3thereof, is positioned a cathode ray gun comprising a cathode 4 enclosedin a beam defining chamber 5, the cathode emission being controlled byan annular grid 6. Immediately over the opening in the annular grid 6 ispositioned the usual anode I having a small conical hollow projection 8extending toward the opening in grid 6.

Spaced from the anode, and between the screen and the anode. is anannular accelerating electrode 9 positioned to surround the beam beforedeflection thereof and before focusing thereof. The construction of theelectrodes 6, l, and 9 including their positioning and the size of theiropenings and the potentials applied thereto, as

explained above, is such that, inherently, the maximum cross section ofthe electron beam is substantially less than the openings in theelectrodes through which the beam passes. Beam deflection isaccomplished by the use of highand low-frequency deflection coil systems10 and l I, respectively, and the beam is maintained in focus onfluorescent screen 2 by means of focusing solenoid l2 energized byfocusing battery IS.

The circuit for placing the device into operation as'an anode modulatedtube is simple.

Annular accelerating electrode 9 is held at a constant positivepotential of, for example, 2000 volts, by voltage source I4. Annulargrid 6 is biased by bias circuit l5, and cathode 4 is heated by cathodesource l5. Conical anode I is connected directly to anode H of finalamplifier tube 18, the grid I? of which is energized by the drop acrossresistor 20 connected to anode 2| of amplifier tube 22, ough couplingcondenser 23. Grid IQ of finaamplifier tube I8 is biased by biasresistor 24 in series with bias battery 25. Grid 26 of first amplifiertube 22 has applied thereto input signals, preferably a train oftelevision signals.

Conical anode l and anode ll of final amplifier tube I8 are bothenergized to the same potential by anode source 21, for example, to 600volts positive, through coupling resistor 28. Thus, anode source 21supplies both the final amplifier tube and the cathode ray tube conicalanode I. The signal to the conical anode is supplied by .the finalamplifier tube [8.

Thus, the cathode ray tube will be anode modulated, with a relativelylow potential on the conical anode. Final acceleration is performed byaccelerating anode 9. The result of modulating the beam by this means isto completely remedy the de-focusing. efiect of signal voltage. Thescanning lines remain constant in width across light-dark boundarieswithout the familiar tailing ou effect common to prior tubes.

The direct coupling of the last amplifier tube to the modulated anodeis, therefore, a distinct advantage in obtaining clearness of finalpicture and constancy of scanning line width. Furthermore, the use ofanode modulation allows grid 0 to be used solely for the regulation ofsuitable background illumination, which regulation may of course be byhand or automatic, in accordance with modern television practice.

, While there has been described what is at present considered thepreferred embodiment of the invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the invention, and it is, therefore,aimed in the appended claims to cover all such changes and modificationsas fall within the true spirit and scope of the invention.

What is claimed is:

l. A cathode-ray tube signal reproducing device comprising an envelope,a target disposed at one end thereof, a cathode disposed at the oppositeend thereof, an apertured grid adjacent said cathode for controlling thenumber of electrons flowing therethrough, a hollow truncated conicalanode adjacent said grid, an annular accelerating anode disposed betweensaid conical anode and said target, means for applying operatingvoltages to said grid and said anodes with a greater voltage beingapplied to said accelerating anode than to said conical anode, said gridand anodes being so proportioned that, when said operating voltages areapplied thereto, the maximum cross section of the electron beam passingthrough said grid and anodes is substantially less than the openingstherein, and means for applying a signal to said conical anode.

2. A cathode-ray tube signal reproducing de- 'vicecomprising a source ofsignal voltage including a vacuum tube having an output electrode, acathode-ray signal reproducing tube including an electron gun having acathode, an apertured grid adapted for limiting the number of electronsflowing therethrough to a predetermined value, a hollow truncatedconical anode for concentrating said limited electrons into a beam andvarying the intensity of said beam, an annular anode for acceleratingsaid defined and modulated beam, a target for receiving said defined andmodulated beam, and means for applying operating potentials to theelectrodes of said tubes including a direct current connection betweensaid vacuum tube output electrode and said first anode whereby signalsare applied directly from said output electrode to said first anode andoperating potentials are applied directly to said two electrodes, saidgrid and anodes being so proportioned that, when said operating voltagesare applied thereto, the maximum cross section of the electron beampassing through said grid and anodes is substantially less than theopenings therein.

BAR'I'HOLOM'EW MOLINARI.

